1. Field of the Invention
This invention is concerned with endodontic filling systems having improved properties over those known to the prior art. More particularly, this invention deals with materials which are useful in endodontic dentistry, especially in root canal filling applications, and with methods and procedures employing such materials for endodontic therapy.
Endodontics or root canal therapy is that branch of dentistry which deals with the diseases of the dental pulp and associated tissues. One aspect of endodontics comprises the treatment of infected root canals, the removal of diseased pulp tissues, followed by the biomechanical modification and the subsequent filling of the pulp canal (root canal). FIG. 1 is a representation of tooth anatomy insofar as it is relevant to an understanding of the present invention.
Those skilled in the art will recognize that root canal therapy is generally indicated for teeth having sound external structures but having diseased, dead or dying pulp tissues. Accordingly, such teeth will generally possess intact enamel 10 and dentin 12, and be satisfactorily engaged with the bony tissue 20, by, inter alia, healthy periodontal ligaments 18. In such teeth, the pulp tissue 14, and excised portions of the root 16, should be replaced by a biocompatible substitute. notice should be taken of the apical foramen 22, the orifice through which blood and nerves pass to support the pulp tissues.
One technique known to those skilled in the art for the preparation of a root canal for filling is represented by figures 2a-2e. A tooth having a basically sound outer structure 24 but diseased pump 26, is cut with conventional dental drill means 28 creating a coronal access opening 30. A broach is used for gross removal of pulp material 26 from the root canal through the coronal access opening 30. The void thus formed is enlarged as in FIG. 2d with reamers and/or files 34, to result in a fully excavated cavity 36. Debris is removed from this cavity by flushing and the cavity cleansed to remove all diseased tissue. Following chemical antisepsis, the escavated canal is ready for filling.
As may be seen in FIG. 3, the prepared canal 36 is not smooth; it comprises numerous lateral spaces such as fissures, accessory canals and cut tubules 38. Some of these irregular structures result from natural morphology while others are artifacts of cavity preparation. It should also be noted that the removal of the pulp tissues effects the removal of the contents of the pump chamber and root canal nearly to the root apex. In practice, however, the apical foramen 22 is occasionally enlarged and some limited subapical space is affected by the preparation.
The filling of prepared root canals has traditionally been accomplished through the use of solid, shaped filling bodies or "points." thus, tapered cones or "points" of silver or gutta percha of the correct size for the canal to be filled are selected, coated with a cement, and placed in the prepared canal. In the case of silver and occasionally gutta percha, a single point may be placed in an attempt to fill the root canal completely. Multiple points of gutta percha may be wedged into a canal to advance the same end. The employment of either silver or gutta percha does not generally result in complete filling of the lateral spaces of the prepared canal. The presence of voids in the filled canal space is believed to foster the growth of bacteria; such incomplete filling is to be avoided. At the same time, it is desirable to control carefully the insertion of root canal filling material and cement to avoid overfilling. Excessive tamping or instrumentation of gutta percha points tends to cause extrusion of the cement used therewith and sometimes the points themselves through the apical foramen into the subapical space. Incorrect placement of a silver point and cement can result in a similar problem. Such extrusion is generally believed to be harmful, to cause irritation of the tissues located at the apex, and to retard the healing thereof.
One attempt to improve the filling efficiency of root canal filling media has employed polymerizable, hydrophilic fluids or pastes. Such fluids or pastes are injected into the prepared root cavity, invading and filling many of the irregularities 38 in the canal. They are then polymerized in situ. While such materials and processes employing them properly address the need for lateral space filling during root canal therapy, certain significant shortcomings are associated therewith. A principle shortcoming in the employment of such polymerizable paste filling formulations in root canal therapy is the tendency of such materials to overfill the cavity. Because of the fluid nature of such pastes, it has been found that significant portions thereof may be extruded through the apical foramen into the subapical space. Additionally, polymerization of such pastes is initially accompanied by a small but significant amount of shrinkage. This shrinkage, approximately 3% of the initial volume, may facilitate the transport of infectious agents and threaten the filled root canal with further microbial attack. The employment of such pastes may also result in the establishment of voids within the filling structure leading to structural inhomogeneity. Swelling then follows polymerization and the initial shrinking, which swelling can result in a net gain in volume of about 8-9% of the initial volume. A further disadvantage is the probable extraction of residual unreacted monomer, plasticizer, accelerator and initiator into the aqueous body fluids.
Further disadvantages also attend the use of such paste filling systems. The employment of endodontic filling pastes presently requires a complex and technically difficult mixing, dispensing, and instrument cleaning routine for use. Thus, the use of such materials requires the mastery of a new therapeutic technique by the endodontic dentist and leads to the likelihood of process errors thereby.
A thorough overview of the State of the Art in endodontic filling materials and processes is presented in "Obturation of the Root Canal System" in Pathways of the Pulp, Cohen et al eds., C.V. Mosby (1980) which is incorporated herein by reference.